Well, I think there is more than one aspect to sin we are talking about here.
1) human nature
2) doing something that is sinful - committing a sin
We all have "human nature" - that is, no-one is perfect. We strive for perfection, but also know we cannot reach it.
Understanding that what you do may be "right" or "wrong" comes as you develop past childhood. Realizing that you are responsible for your actions comes through time, obviously. Again, I cannot say it is whenever a child turns, say, 12 years old. It is based on the individual and their development.
When we look at children, we realize that they may do things that, as an adult, would be irresponsible, perhaps cruel, perhaps just silly. But they do not have the understanding of the full consequences of their actions.
Just because it does not seem logical or straightforward does not mean it's "twisted" or "double minded". I don't think anyone pretends that faith, and the nature of the world, and the nature of people, is completely logical, no matter what the faith. I didn't intend to start this thread as to say "mine is better" or "yours is better", but to try and understand the differences. The faith I am a part of draws heavily on early church history and teachings, so there is more closeness in perspective than perhaps you may think.